Methods for forming conductive titanium oxide thin films

ABSTRACT

The present disclosure relates to the deposition of conductive titanium oxide films by atomic layer deposition processes. Amorphous doped titanium oxide films are deposited by ALD processes comprising titanium oxide deposition cycles and dopant oxide deposition cycles and are subsequently annealed to produce a conductive crystalline anatase film. Doped titanium oxide films may also be deposited by first depositing a doped titanium nitride thin film by ALD processes comprising titanium nitride deposition cycles and dopant nitride deposition cycles and subsequently oxidizing the nitride film to form a doped titanium oxide film. The doped titanium oxide films may be used, for example, in capacitor structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. Pat. No. 6,660,660 to Haukka et al,filed Aug. 31, 2001, entitled Methods for Making a Dielectric Stack inan Integrated Circuit, and U.S. Pat. No. 7,045,406 to Huotari et al,filed May 5, 2003, entitled method of Forming an Electrode with AdjustedWork Function, and U.S. Pat. No. 6,858,524 to Haukka et al, filed May 5,2003, entitled Method of Depositing Barrier Layer from Metal Gates. Theentire disclosure of each of these references is incorporated byreference herein.

PARTIES OF JOINT RESEARCH AGREEMENT

The invention claimed herein was made by, or on behalf of, and/or inconnection with a joint research agreement between the University ofHelsinki and ASM Microchemistry Oy signed on Nov. 14, 2003. Theagreement was in effect on and before the date the claimed invention wasmade, and the claimed invention was made as a result of activitiesundertaken within the scope of the agreement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present application relates generally to atomic layer deposition ofconductive titanium oxide thin films. The conductive titanium oxidefilms may serve, for example, as an interface layer between a high kmaterial and a metal electrode.

2. Background

Transparent conducting oxides are used in a wide variety ofapplications, including flat panel displays, light emitting diodes andsolar cells. Sn-doped In₂O₃ (ITO) has been commonly used but suffersfrom some drawbacks. Recently, it has been found that the conductivityof TiO₂ can be increased by doping with niobium or tantalum. These dopedanatase thin films have a resistivity value comparable to conventionalITO, making TiO₂:Nb and TiO₂:Ta candidates for a new transparentconducting oxide.

ALD is a self-limiting process, whereby alternated pulses of reactionprecursors saturate a substrate surface and leave no more than onemonolayer of material per pulse. The deposition conditions andprecursors are selected to ensure self-saturating reactions, such thatan adsorbed layer in one pulse leaves a surface termination that isnon-reactive with the gas phase reactants of the same pulse. Asubsequent pulse of different reactants reacts with the previoustermination to enable continued deposition. Thus, each cycle ofalternated pulses leaves typically less or no more than about onemolecular layer of the desired material. The principles of ALD typeprocesses have been presented by T. Suntola, e.g. in the Handbook ofCrystal Growth 3, Thin Films and Epitaxy, Part B: Growth Mechanisms andDynamics, Chapter 14, Atomic Layer Epitaxy, pp. 601-663, ElsevierScience B.V. 1994, the disclosure of which is incorporated herein byreference. Variations of ALD have been proposed that allow formodulation of the growth rate. However, to provide for high conformalityand thickness uniformity, these reactions are still more or lessself-saturating.

Atomic layer deposition of conducting oxides has focused mainly on SnO₂,ITO and ZnO. These materials contain elements that are uncommon inintegrated circuits (ICs) and zinc in particular is not used in the ICcontext. ALD of mixed titanium oxide films has thus far been concernedwith improving the insulating properties of the films, not withpreparing conductive films.

SUMMARY

A need therefore exists for controllable and reliable methods forforming conductive titanium oxide thin films. In accordance with oneaspect of the present invention, methods for forming doped titaniumoxide thin films on a substrate in a reaction chamber by atomic layerdeposition (ALD) are provided. In some embodiments, the methods includea titanium oxide deposition cycle comprising: providing a vapor phasereactant pulse comprising a titanium precursor into the reaction chamberto form no more than about a single molecular layer of the titaniumprecursor on the substrate, removing excess reactant from the reactionchamber, providing a vapor phase reactant pulse comprising an oxygenprecursor to the reaction chamber such that the oxygen precursor reactswith the titanium precursor on the substrate, and removing excess secondreactant and any reaction byproducts from the reaction chamber. Themethods also include dopant oxide deposition cycles comprising:providing a vapor phase reactant pulse comprising a niobium or tantalumprecursor to the reaction chamber, removing excess reactant from thereaction chamber, providing a vapor phase reactant pulse comprising anoxygen precursor to the reaction chamber such that the oxygen precursorreacts with the niobium or tantalum precursor on the substrate, andremoving excess reactant and any reaction byproducts from the reactionchamber. The titanium oxide and dopant oxide deposition cycles arerepeated until a thin film of a desired thickness and composition isobtained. In some embodiments the doped titanium oxide layer issubsequently annealed to form a conductive titanium oxide thin film.

In accordance with another aspect of the present invention, methods forforming memory capacitors in integrated circuits are provided. Themethods typically comprise: depositing a bottom electrode, depositing aconductive titanium oxide layer doped with a group V (for example V, Nb,Ta) metal by ALD on the bottom electrode, depositing an ultra-high-klayer directly over and contacting the titanium oxide layer, anddepositing a top electrode directly over and contacting the ultra-high-klayer.

In accordance with another aspect of the present invention, methods forforming doped titanium oxide thin films on a substrate in a reactionchamber by atomic layer deposition (ALD) are provided. In someembodiments, the methods include titanium nitride deposition cycles anddopant nitride deposition cycles that are repeated in a ratio thatproduces a doped oxide film with the desired composition and thickness.

The titanium nitride deposition cycle may comprise: providing a vaporphase first reactant pulse comprising a titanium precursor into thereaction chamber to form no more than about a single molecular layer ofthe titanium precursor on the substrate, removing excess first reactantfrom the reaction chamber, providing a vapor phase second reactant pulsecomprising a nitrogen precursor to the reaction chamber such that thenitrogen precursor reacts with the titanium precursor on the substrate,and removing excess second reactant and any reaction byproducts from thereaction chamber. The dopant nitride deposition cycles may comprise:providing a vapor phase first reactant pulse comprising a dopantprecursor, such as a niobium or tantalum precursor to the reactionchamber, removing excess first reactant from the reaction chamber,providing a vapor phase second reactant pulse comprising a nitrogenprecursor to the reaction chamber such that the nitrogen precursorreacts with the niobium or tantalum precursor on the substrate, andremoving excess second reactant and any reaction byproducts from thereaction chamber. The titanium nitrogen and dopant nitride depositioncycles are repeated at a ratio that produces a thin film of a desiredthickness and composition. In some embodiments, the doped titaniumnitride thin film is oxidized to form a doped titanium oxide thin filmThe doped titanium oxide layer may be subsequently annealed to form aconductive titanium oxide thin film.

In accordance with another aspect of the present invention, methods forforming memory capacitors in integrated circuits are provided. In someembodiments, the methods typically comprise: depositingTi_(1−x)Nb_(x)N_(y) or Ti_(1−x)Ta_(x)N_(y); forming a bottom electrodeor interfacial layer by converting at least a portion of theTi_(1−x)Nb_(x)N_(y) or Ti_(1−x)Ta_(x)N_(y) to a conductive layercomprising Ti_(1−x)Nb_(x)O_(y) or Ti_(1−x)Ta_(x)O_(y); depositing anultra-high-k layer; and depositing a top electrode directly over andcontacting the ultra-high-k layer.

For purposes of summarizing the invention and the advantages achievedover the prior art, certain objects and advantages of the invention havebeen described herein above. Of course, it is to be understood that notnecessarily all such objects or advantages may be achieved in accordancewith any particular embodiment of the invention. Thus, for example,those skilled in the art will recognize that the invention may beembodied or carried out in a manner that achieves or optimizes oneadvantage or group of advantages as taught herein without necessarilyachieving other objects or advantages as may be taught or suggestedherein.

All of these embodiments are intended to be within the scope of theinvention herein disclosed. These and other embodiments of the presentinvention will become readily apparent to those skilled in the art fromthe following detailed description of the preferred embodiments havingreference to the attached figures, the invention not being limited toany particular preferred embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart generally illustrating a method for forming aniobium or tantalum doped titanium oxide thin film in accordance withone embodiment;

FIG. 2 is a flow chart generally illustrating a method for forming amemory capacitor in an integrated circuit in accordance with oneembodiment;

FIG. 3 is a graph illustrating cation ratios for TiNbO and TiTaO filmsas a function of ALD pulsing ratio;

FIG. 4 is a graph illustrating resistivities of TiNbO and TiTaO filmsformed by ALD;

FIG. 5 is an x-ray diffractogram of a TiO₂ and TiO₂ film doped withniobium prepared by ALD;

FIG. 6 is a field emission scanning electron microscope (FESEM) image ofa Ti_(0.69)Nb_(0.31)O₂ film after annealing in forming gas at 600° C.;

FIG. 7 is a graph illustrating the optical transmittance of aTi_(0.69)Nb_(0.31)O₂ thin film formed by ALD after annealing;

FIG. 8 is a graph illustrating x-ray diffractogram data for TiNbO thinfilms formed by ALD;

FIG. 9 is a graph illustrating resistivities for TiNbO thin films formedby ALD under different deposition and annealing conditions; and

FIG. 10 is a graph illustrating resistivities for TiNbO thin filmsformed by ALD on different substrates.

DETAILED DESCRIPTION

While illustrated in the context of forming a conductive interface filmin memory capacitors, the skilled artisan will readily appreciate theapplication of the principles and advantages disclosed herein to variouscontexts in which conductive titanium oxide films are useful. Forexample, conductive, transparent titanium oxide films can be used inflat panel displays, LEDs and solar cells.

Conductive doped titanium oxide thin films can be deposited on asubstrate by atomic layer deposition (ALD) type processes. In someembodiments, amorphous films of TiO₂ and an oxide of the dopant arealternately deposited by ALD. The films are then annealed to crystallizeto the anatase phase. For example, alternating layers of amorphous TiO₂and Nb₂O₅ can be deposited by ALD and then annealed. In otherembodiments, alternating layers of amorphous TiO₂ and Ta₂O₅ aredeposited by ALD and annealed. The thickness of each of the layers canbe selected to produce a doped conductive TiO₂ film with the desiredcomposition and resistivity, that is, not necessarily a 1:1 ratio oftitanium oxide and dopant oxide cycles.

ALD type processes are based on controlled, self-limiting surfacereactions of precursor chemicals. Gas phase reactions are avoided byfeeding the precursors alternately and sequentially into the reactionchamber. Vapor phase reactants are separated from each other in thereaction chamber, for example, by removing excess reactants and/orreactant byproducts from the reaction chamber between reactant pulses.

Briefly, a substrate is loaded into a reaction chamber and is heated toa suitable deposition temperature, generally at lowered pressure.Deposition temperatures are maintained below the thermal decompositiontemperature of the reactants but at a high enough level to avoidcondensation of reactants and to provide the activation energy for thedesired surface reactions. Of course, the appropriate temperature windowfor any given ALD reaction will depend upon the surface termination andreactant species involved. Here, the temperature is preferably at orbelow about 300° C., more preferably at about 200° C.

A first reactant is conducted or pulsed into the chamber in the form ofvapor phase pulse and contacted with the surface of the substrate.Conditions are preferably selected such that no more than about onemonolayer of the first reactant is adsorbed on the substrate surface ina self-limiting manner. The appropriate pulsing times can be readilydetermined by the skilled artisan based on the particular circumstances.Excess first reactant and reaction byproducts, if any, are removed fromthe reaction chamber, such as by purging with an inert gas.

Purging the reaction chamber means that vapor phase precursors and/orvapor phase byproducts are removed from the reaction chamber such as byevacuating the chamber with a vacuum pump and/or by replacing the gasinside the reactor with an inert gas such as argon or nitrogen. Typicalpurging times are from about 0.05 to 20 seconds, more preferably betweenabout 1 and 10, and still more preferably between about 1 and 2 seconds.However, other purge times can be utilized if necessary, such as wherehighly conformal step coverage over extremely high aspect ratiostructures or other structures with complex surface morphology isneeded. Also, batch ALD reactors can utilize longer purging timesbecause of increased volume and surface area.

A second gaseous reactant is pulsed into the chamber where it reactswith the first reactant bound to the surface. Excess second reactant andgaseous byproducts of the surface reaction are removed from the reactionchamber, preferably by purging with the aid of an inert gas and/orevacuation. The steps of pulsing and purging are repeated until a thinfilm of the desired thickness has been formed on the substrate, witheach cycle leaving typically less than or no more than a molecularmonolayer.

As mentioned above, each pulse or phase of each cycle is preferablyself-limiting. An excess of reactants is supplied in each phase tosaturate the susceptible structure surfaces. Surface saturation ensuresreactant occupation of all available reactive sites (subject, forexample, to physical size or “steric hindrance” restraints) and thusensures excellent step coverage.

FIG. 1 is a flow chart generally illustrating a method for forming aniobium or tantalum doped titanium oxide thin film in accordance withone embodiment. According to a preferred embodiment, an amorphoustitanium oxide thin film is formed on a substrate by an ALD type process100 comprising multiple titanium oxide and dopant deposition cycles,each titanium oxide deposition cycle comprising:

-   -   providing a first vapor phase reactant pulse comprising a        titanium precursor into the reaction chamber to form no more        than about a single molecular layer of the titanium precursor on        the substrate;    -   removing excess first reactant from the reaction chamber;    -   providing a second vapor phase reactant pulse comprising an        oxygen precursor to the reaction chamber such that the oxygen        precursor reacts with the titanium precursor on the substrate;    -   removing excess second reactant and reaction byproducts, if any,        from the reaction chamber.

This can be referred to as the titanium oxide deposition cycle. In someembodiments the process begins with a titanium oxide deposition cycle.First, a vapor phase titanium precursor is provided to the substrate andreaction space 110. The titanium precursor is preferably an alkoxide,halide, alkylamine, betadiketonate, cyclopentadienyl, orcyclopentadienyl derivative compound. Preferred alkoxides includeTi(OMe)₄ and Ti(OiPr)₄. Preferred halides include compounds having theformula TiX₄, where X is a halogen, such as TiCl₄, TiBr₄, TiF₄, andTiI₄. Preferably, the titanium precursor is provided such that it formsno more than about a single molecular layer of titanium precursor on thesubstrate. If necessary, any excess titanium precursor can be purged orremoved 120 from the reaction space. In some embodiments, the purge stepcan comprise stopping the flow of titanium precursor while stillcontinuing the flow of an inert carrier gas such as nitrogen or argon.Next, an oxygen source or precursor is provided 130 to the substrate andreaction chamber. Any of a variety of oxygen precursors can be used,including, without limitation: oxygen, plasma excited oxygen, atomicoxygen, ozone, water, etc. Preferably, the oxygen source is H₂O orozone. A suitable oxygen precursor can be selected by the skilledartisan such that it reacts with the molecular layer of the titaniumprecursor on the substrate to form titanium oxide. Each titanium oxidedeposition cycle typically forms less than or no more than about onemolecular layer of titanium oxide. If necessary, any excess reactionbyproducts or oxygen precursor can be removed 140 from the reactionspace. In some embodiments, the purge step can comprise stopping theflow of oxygen precursor while still continuing the flow of an inertcarrier gas such as nitrogen or argon.

The titanium oxide deposition cycle is typically repeated apredetermined number of times. In some embodiments, multiple molecularlayers of titanium oxide are formed by multiple deposition cycles. Inother embodiments, a molecular layer or less of titanium oxide isformed.

In order to dope the titanium oxide with a dopant such as Nb or Ta, thetitanium deposition cycles are alternated with deposition of an oxidecomprising the desired dopant, such as Nb₂O₅ or Ta₂O₅. Thus, a secondALD cycle is performed, which can be referred to as the dopant oxidedeposition cycle.

According to some embodiments, the dopant oxide deposition cyclepreferably comprises:

-   -   providing a vapor phase reactant pulse comprising a niobium or        tantalum precursor to the reaction chamber;    -   removing excess reactant from the reaction chamber, if any;    -   providing a vapor phase reactant pulse comprising an oxygen        precursor to the reaction chamber such that the oxygen precursor        reacts with the niobium or tantalum precursor on the substrate;        and    -   removing excess reactant and any reaction byproducts from the        reaction chamber.

The titanium oxide cycle and dopant oxide cycles are repeated until athin film of a desired thickness and composition comprisingTi_(1−x)Nb_(x)O_(y) or Ti_(1−x)Ta_(x)O_(y), wherein x is between zeroand one and wherein y is approximately 2, is obtained.

Also, if the desired film composition and thickness 145 is not met aftera deposition cycle then a next step can include providing a vapor phasereactant pulse comprising a titanium precursor 110 or to perform adopant oxide deposition cycle beginning with step 150, providing a vaporphase reactant pulse comprising a niobium or tantalum precursor.

Multiple titanium oxide layers can also be formed on top of each otheror formed in a desired pattern with the dopant oxide layers, such asalternating layers or two titanium oxide layers for every dopant layer,etc. In some embodiments, the TiO₂ deposition cycle is repeated for 1 to100 times and more preferably 1 to 10 and most preferably 1 to 4 timesfor each dopant oxide cycle. In some embodiments, repeat TiO₂ and dopantoxide cycles multiple times before moving to the other. For example,repeating the TiO₂ oxide cycle ten times then three cycles of the dopantoxide deposition cycle. In some embodiments, after a doped titaniumoxide thin film is deposited to a desired thickness the thin film can beannealed.

In some embodiments, Nb is used as a dopant. The titanium oxide layerscan be formed according to the cycles described herein. A niobiumprecursor is selected from any suitable niobium precursor. Preferably,the niobium precursor or source is an alkoxide such as Nb(OEt)₅ orhalide such as NbCl₅, NbF₅. In some embodiments, the niobium precursoris an alkylamine. The skilled artisan can select an appropriate niobiumprecursor such that it forms no more than about one molecular layer ofniobium precursor on the substrate under the reactive conditions. Withcontinued reference to FIG. 1, the niobium precursor is then provided150 to the reaction chamber such that no more than about a singlemolecular layer of the niobium precursor is adsorbed on the substrate.If necessary, any excess niobium precursor can be purged or removed 160from the reaction space. In some embodiments, the removal step 160 cancomprise stopping the flow of niobium precursor while still continuingthe flow of an inert carrier gas, such as nitrogen. Next, an oxygenprecursor is provided to the reaction space 170 such that the oxygenprecursor reacts with the niobium precursor on the substrate. Next, anyexcess oxygen source reactant and/or any reaction byproducts can bepurged 180 or removed from the reaction space. In some embodiments, thepurge step can comprise stopping the flow of oxygen precursor whilestill continuing the flow of an inert carrier gas, such as nitrogen orargon. Depending on the desired film composition and thickness 185 thereare many options for proceeding after a layer of niobium oxide layer isformed, including: forming another niobium oxide layer, forming atitanium oxide layer by performing a titanium oxide deposition cycle,forming a tantalum oxide layer, or the thin film can be annealed 190.

In some embodiments, Ta is used as a dopant. The titanium oxide layerscan be formed according to the cycles described herein. A tantalum oxide(Ta₂O₅) layer can be formed directly on top of a titanium oxide layer ordopant oxide layer. First, a tantalum precursor is selected from avariety of suitable tantalum precursors. Preferably, the tantalumprecursor or source is an alkoxide, halide, or amine derivative.Preferred alkoxides include Ta(OEt)₅. Preferred halides includecompounds having the formula TaX₅, wherein X is a halide, such as TaCl₅,TaF₅, and TaBr₅. Preferred amine derivatives include alkylamines, forexample pentakis(dimethylamino)tantalum (PDMAT), tertiary amylimido-tris-dimethylamido tantalum (TAIMATA), andtert-butylimidotris(diethylamido)tantalum (TBTDET). The skilled artisancan select an appropriate tantalum precursor such that it forms no morethan about one molecular layer of tantalum precursor on the substrate.With continued reference to FIG. 1, the tantalum precursor is thenprovided 150 to the reaction chamber such that no more than about asingle molecular layer of the tantalum precursor is adsorbed on thesubstrate. If necessary, any excess tantalum precursor can be purged orremoved 160 from the reaction space. In some embodiments, the removalstep 160 can comprise stopping the flow of tantalum precursor whilestill continuing the flow of an inert carrier gas such as nitrogen.Next, an oxygen precursor is provided to the reaction space 170 suchthat the oxygen precursor reacts with the tantalum precursor on thesubstrate. Next, any excess oxygen source reactant and/or any reactionbyproducts can be purged 180 or removed from the reaction space. In someembodiments, the purge step can comprise stopping the flow of oxygenprecursor while still continuing the flow of an inert carrier gas suchas nitrogen or argon. Depending on the desired film composition andthickness 185 there are many options for proceeding after a layer oftantalum oxide is formed, including: forming another tantalum oxidelayer, forming a titanium oxide layer by performing a titanium oxidedeposition cycle, forming a niobium oxide layer, or the thin film can beannealed 190.

The dopant oxide deposition cycle is typically repeated a predeterminednumber of times. In some embodiments, multiple molecular layers ofdopant oxide are formed by multiple deposition cycles. In otherembodiments, a molecular layer or less of dopant oxide is formed.

However, in some embodiments less than a complete continuous layer ofdopant oxide is deposited. If the film is of a desired thickness andcomposition 185 then the thin film can be annealed 190, discussed ingreater detail below.

Removing excess reactants can include evacuating some of the contents ofthe reaction space or purging the reaction space with helium, nitrogenor any other inert gas. In some embodiments purging can comprise turningoff the flow of the reactive gas while continuing to flow an inertcarrier gas to the reaction space.

The number of titanium oxide deposition cycles and dopant oxidedeposition cycles can be selected to produce a film of the desiredcomposition and/or resistivity. Typically, the ratio of titanium oxidecycles (consisting of titanium-containing precursor followed by oxygensource pulses) to dopant oxide cycles (consisting of a dopant sourcefollowed by the corresponding oxygen source pulses) is about 200:1 toabout 1:20, preferably about 100:1 to 1:10, more preferably about 50:1to about 1:3, and even more preferably 10:1 to 1:1. FIG. 3 illustratescation ratios for TiNbO and TiTaO films as a function of the ALD pulsingratio with dopant pulsing ratios illustrated for cation molarconcentrations between about 0% to about 50%. The data illustrated inFIG. 3 corresponds to Ti_(1−x)Nb_(x)O₂ thin films with x values betweenabout 0.0 and about 0.50. In some embodiments, x values are around 0.3.

Deposition may begin and end with a titanium oxide deposition cycle or adopant oxide deposition cycle. For example, the growth can be startedwith the deposition of titanium oxide and ended with the deposition ofdopant oxide. In other embodiments, growth can be started with titaniumoxide and ended with titanium oxide.

The precursors employed in the ALD type processes may be solid, liquidor gaseous material under standard conditions (room temperature andatmospheric pressure), provided that the precursors are in vapor phasebefore it is conducted into the reaction chamber and contacted with thesubstrate surface. “Pulsing” a vaporized precursor onto the substratemeans that the precursor vapor is conducted into the chamber for alimited period of time. Typically, the pulsing time is from about 0.05to 10 seconds. However, depending on the substrate type and its surfacearea, the pulsing time may be even higher than 10 seconds. Preferably,for a 300 mm wafer in a single wafer ALD reactor, a metal precursor,such as a Ti, Ta or Nb precursor, is pulsed for from 0.05 to 10 seconds,more preferably for from 0.1 to 5 seconds and most preferably for about0.3 to 3.0 seconds. An oxygen-containing precursor is preferably pulsedfor from about 0.05 to 10 seconds, more preferably for from 0.1 to 5seconds, most preferably about for from 0.2 to 3.0 seconds. However,pulsing times can be on the order of minutes in some cases. The optimumpulsing time can be readily determined by the skilled artisan based onthe particular circumstances.

Suitable dopant precursors may be selected by the skilled artisan. Ingeneral, metal compounds where the metal is bound or coordinated to ahalide, oxygen, nitrogen, carbon or a combination thereof are preferred.In some embodiments the metal precursors are organic compounds. Inanother embodiment the metal precursors are halides. In yet anotherembodiment, all Ti or Ta and dopant precursors are halides, preferablychlorides.

The oxygen source may be an oxygen-containing gas pulse and can be amixture of oxygen and inactive gas, such as nitrogen or argon. In someembodiments the oxygen source may be a molecular oxygen-containing gaspulse. One source of oxygen may be air. In preferred embodiments, theoxygen source or precursor is water. In some embodiments the oxygensource comprises an activated or excited oxygen species. In someembodiments the oxygen source comprises ozone. The oxygen source may bepure ozone or a mixture of ozone and another gas, for example aninactive gas such as nitrogen or argon. In other embodiments the oxygensource is oxygen plasma.

The oxygen precursor pulse may be provided, for example, by pulsingozone or a mixture of ozone and another gas into the reaction chamber.In other embodiments, ozone is formed inside the reactor, for example byconducting oxygen containing gas through an arc. In other embodiments anoxygen containing plasma is formed in the reactor. In some embodimentsthe plasma may be formed in situ on top of the substrate or in closeproximity to the substrate. In other embodiments the plasma is formedupstream of the reaction chamber in a remote plasma generator and plasmaproducts are directed to the reaction chamber to contact the substrate.As will be appreciated by the skilled artisan, in the case of remoteplasma the pathway to the substrate can be optimized to maximizeelectrically neutral species and minimize ion survival before reachingthe substrate.

The mass flow rate of the precursors can also be determined by theskilled artisan. In one embodiment, for deposition on 300 mm wafers theflow rate of metal precursors is preferably between about 1 and 1000sccm without limitation, more preferably between about 100 and 500 sccm.The mass flow rate of the metal precursors is usually lower than themass flow rate of the oxygen source, which is usually between about 10and 10000 sccm without limitation, more preferably between about100-2000 sccm and most preferably between 100-1000 sccm.

The pressure in the reaction chamber is typically from about 0.01 and 20mbar, more preferably from about 1 to about 10 mbar. However, in somecases the pressure will be higher or lower than this range, as can bereadily determined by the skilled artisan.

Before starting the deposition of the film, the substrate is typicallyheated to a suitable growth temperature. Preferably, the growthtemperature of the metal oxide thin film is less than about 300° C.,more preferably less than about 250° C. and even more preferably lessthan about 200° C. Typically, the growth temperature is less than thecrystallization temperature for the deposited materials such that anamorphous thin film is formed. The preferred deposition temperature mayvary depending on a number of factors such as, and without limitation,the reactant precursors, the pressure, flow rate, the arrangement of thereactor, crystallization temperature of the deposited thin film, and thecomposition of the substrate including the nature of the material to bedeposited on. The specific growth temperature may be selected by theskilled artisan using routine experimentation.

The deposition cycles can be repeated a predetermined number of times oruntil a desired thickness is reached. Preferably, the thin films arebetween about 2 nm and 200 nm thick.

Following deposition, layers comprising mostly amorphous titanium oxideand dopant oxide are annealed to crystallize the film to the anatasephase, resulting in an electrically conductive titanium oxide anatasefilm. However, as-deposited films are somewhat electrically conductiveand in some cases those could be used without annealing. Thus, anamorphous structure is first provided and the conductive phase can beobtained by annealing in the presence of an inert atmosphere (such as anitrogen atmosphere), an oxygen-free atmosphere, or a reducingatmosphere, such as a forming gas atmosphere (5% hydrogen 95% nitrogen),at temperatures of at least 400° C., in particular in between about 500°C. and 800° C., and preferably about 600° C. These temperatures andatmospheres are similar to annealing temperatures and atmospheres forSrTiO₃, BaTiO₃ and (Sr,Ba)TiO₃. Typically, annealing lasts from a fewminutes to more than an hour depending on the thickness of the thin filmand annealing process conditions. Ultra-thin films of a few nanometersthick may crystallize in seconds. The composition of the films and theresistivity can be controlled by adjusting the thickness of the layersand the concentration of dopant.

FIG. 4 illustrates the resistivities of various TiNbO and TiTaO thinfilms after annealing for 30 minutes in forming gas (5% hydrogen/95%nitrogen) at 600° C. The y-axis represents resistivity in Ωcm and thex-axis represents the atomic ratio of dopant, represented by M, to totalamount of metal (M+Ti). The lowest resistivity of 0.0019 Ωcm wasmeasured for a Ti_(0.69)Nb_(0.31)O₂ thin film. The Ti_(1−x)Nb_(x)O₂ thinfilms with x values between about 0.20 and 0.40 had the lowestresistivities after annealing. Generally, the titanium oxide thin filmsdoped with niobium had lower resistivities than the thin films dopedwith tantalum.

Anatase titanium oxide also has enhanced optical transmissionproperties. Titanium oxide in the anatase phase has good opticaltransmission properties making it transparent. In some embodiments,doped titanium oxide thin films in the anatase phase can have opticaltransmittance greater than about 60% in the visible region. Opticaltransmittance can be measured, for example, by using aUV/VIS-spectrometer. The optical transmittance of an exemplaryTi_(0.69)Nb_(0.31)O₂ thin film is illustrated in FIG. 7 and discussed ingreater detail below.

In some embodiments, electrically conductive Ti_(1−x)Nb_(x)O_(y) orTi_(1−x)Ta_(x)O_(y) thin films are formed by oxidizing correspondingdoped nitrides, such as Ti_(1−x)Nb_(x)N_(y) or Ti_(1−x)Ta_(x)N_(y). Insome embodiments, a doped nitride thin film is deposited by an ALD typeprocess. The doped nitride film may comprise, for example,Ti_(1−x)Nb_(x)N_(y) or Ti_(1−x)Ta_(x)N_(y). Preferably, the dopednitride thin film is deposited by an ALD type process comprising atitanium nitride deposition cycle and a dopant nitride deposition cycle.The titanium deposition cycle preferably comprises alternating andsequential pulses of a titanium source and nitrogen source. In someembodiments, the titanium nitride deposition cycle comprises:

-   -   providing a first vapor phase reactant pulse comprising a        titanium precursor into the reaction chamber to form no more        than about a single molecular layer of the titanium precursor on        the substrate;    -   removing excess first reactant from the reaction chamber;    -   providing a second vapor phase reactant pulse comprising a        nitrogen precursor to the reaction chamber such that the        nitrogen precursor reacts with the titanium precursor on the        substrate;    -   removing excess second reactant and reaction byproducts, if any,        from the reaction chamber.

The titanium precursor is preferably halide, alkylamine, betadiketonate,cyclopentadienyl, or cyclopentadienyl derivative compound. Preferredhalides include compounds having the formula TiX₄, where X is a halogen,such as TiCl₄, TiBr₄, TiF₄, and TiI₄. Preferably, the titanium precursoris provided such that it forms no more than about a single molecularlayer of titanium precursor on the substrate. If necessary, any excesstitanium precursor can be purged or removed from the reaction space.

Suitable nitrogen precursors include, but are not limited to: NH₃,NH₃-plasma and radicals, N₂/H₂-plasma and radicals, atomic N and H, andammonia derivatives, such as hydrazine. Preferably, the nitrogen sourceis ammonia. A suitable nitrogen precursor can be selected by the skilledartisan such that it reacts with the molecular layer of the titaniumprecursor on the substrate to form titanium nitride.

Each titanium nitride deposition cycle typically forms about a fractionof one molecular layer of titanium nitride. If necessary, any excessreaction byproducts or nitrogen precursor can be removed from thereaction space. In some embodiments, the purge steps, in which excessreactant and/or reaction byproducts are removed from the reactionchamber, can comprise stopping the flow of a reactant while stillcontinuing the flow of an inert carrier gas such as nitrogen or argon.

The titanium nitride deposition cycle is typically repeated apredetermined number of times relative to each dopant nitride depositioncycle. In some embodiments, multiple molecular layers of titaniumnitride are formed by multiple titanium nitride deposition cycles priorto a dopant nitride deposition cycle. In other embodiments, a molecularlayer or less of titanium nitride is formed.

In order to dope the titanium nitride with a dopant such as Nb or Ta,the titanium nitride deposition cycles are alternated with deposition ofa nitride comprising the desired dopant, such as NbN, NbN_(x), Nb₃N₅,TaN, TaN_(x) or Ta₃N₅. Thus, a second ALD cycle can be referred to asthe dopant nitride deposition cycle.

According to some embodiments, the dopant nitride deposition cyclepreferably comprises:

-   -   providing a first vapor phase reactant pulse comprising a        niobium or tantalum (or other dopant) precursor to the reaction        chamber;    -   removing excess first reactant from the reaction chamber, if        any;    -   providing a second vapor phase reactant pulse comprising a        nitrogen precursor to the reaction chamber such that the        nitrogen precursor reacts with the niobium or tantalum precursor        on the substrate; and    -   removing excess second reactant and any reaction byproducts from        the reaction chamber.

The titanium nitride cycle and dopant nitride cycles are repeated for aperiod of time and at a ratio such that a thin film of a desiredthickness and composition is obtained. The number of titanium nitridedeposition cycles and dopant nitride deposition cycles in the processcan be selected to produce a film of the desired composition and/orresistivity. In some embodiments the thin film comprisesTi_(1−x)Nb_(x)N_(y) or Ti_(1−x)Ta_(x)N_(y) wherein x is between zero andone and wherein y is between about 1 and about 2. The order and ratio oftitanium nitride to dopant nitride cycles can be varied based on thedesired x and y values of the resulting Ti_(1−x)Nb_(x)N_(y) orTi_(1−x)Ta_(x)N_(y) thin film.

Typically, the ratio of titanium nitride cycles (consisting oftitanium-containing precursor followed by nitrogen source pulses) todopant nitride cycles (consisting of a dopant source followed by thecorresponding nitrogen source pulses) is about 200:1 to about 1:20,preferably about 100:1 to 1:10, more preferably about 50:1 to about 1:3,and even more preferably 10:1 to 1:1.

In some embodiments the process begins with a titanium nitridedeposition cycle while in other embodiments the process may begin with adopant nitride deposition cycle. Similarly, the process may end witheither a titanium nitride or dopant nitride deposition cycle.

Also, if the desired film composition and thickness is not met after aparticular deposition cycle then a next step can include beginninganother titanium nitride deposition cycle by providing a vapor phasereactant pulse comprising a titanium precursor or beginning anotherdopant nitride deposition cycle by providing a vapor phase reactantpulse comprising a niobium or tantalum precursor.

Multiple titanium nitride layers can also be formed on top of each otheror formed in a desired pattern with the dopant nitride layers, such asalternating layers or two titanium nitride layers for every dopantlayer, etc. In some embodiments, the titanium nitride deposition cycleis repeated 1 to 100 times and more preferably 1 to 10 and mostpreferably 1 to 4 times for each dopant nitride cycle. In someembodiments, the titanium nitride and dopant nitride cycles are repeatedmultiple times before moving to the other. For example, the titaniumnitride cycle can be repeated ten times followed by three cycles of thedopant nitride deposition cycle. The dopant nitride deposition cycle istypically repeated a predetermined number of times. In some embodiments,multiple molecular layers of dopant nitride are formed by multipledeposition cycles. In other embodiments, a molecular layer or less ofdopant nitride is formed.

In some embodiments, after a doped titanium nitride thin film isdeposited to a desired thickness the thin film can be annealed asdescribed above.

Suitable Nb and Ta precursors for the dopant nitride deposition cycleare described above in the description of the dopant oxide depositioncycle. Suitable nitrogen precursors include, but are not limited to:NH₃, NH₃-plasma and radicals, N₂/H₂-plasma and radicals, atomic N and H,and ammonia derivatives, such as hydrazine.

In both the titanium nitride and dopant nitride deposition cycles,removing excess reactants can include evacuating some of the contents ofthe reaction space or purging the reaction space with helium, nitrogenor any other inert gas. In some embodiments purging can comprise turningoff the flow of a reactant gas while continuing to flow an inert carriergas to the reaction space.

Once a doped thin film of the desired composition is formed, the filmcan be further processed depending on the desired properties of the thinfilm. In some embodiments, all or part of the thin Ti_(1−x)Nb_(x)N_(y)or Ti_(1−x)Ta_(x)N_(y) thin film can be oxidized. The thin film can beoxidized using oxygen sources including, without limitation: water,ozone, oxygen, oxygen plasma, oxygen radicals, atomic oxygen, alcohol,and H₂O₂.

In some embodiments the thin film is oxidized in a separate oxidationstep by exposure to an oxidant. A wide range of temperatures and timescan be used in an oxidation step depending on the specific oxidant anddesired thickness of the oxide layer. Preferably the temperature duringthe oxidation step is between 20° C. and 500° C. For example, in someembodiments with oxygen sources such as, ozone, oxygen plasma, oxygenradicals and atomic oxygen oxidation can occur at room temperature (20°C.) or even below 20° C. The temperature for oxidation with oxygen,water, alcohol, and H₂O₂ is preferably from about 20° C. to 1000° C.,more preferably from about 100° C. to about 800° C. and most preferablyfrom about 100° C. to 500° C. The oxidation step time depends on thetemperature and oxygen source. The oxidation step can occur on the orderof seconds or minutes, preferably from 0.1 to 180 seconds, morepreferably from 1 to 60 seconds.

In other embodiments, the doped titanium nitride thin film is oxidizedduring deposition of the next layer, such as an ultra-high-k layer. Insome embodiments, the doped titanium nitride thin film is oxidizedduring an annealing step.

In some embodiments, the thin film can be annealed after it is oxidized.Annealing the thin film after oxidation can increase the crystallinityof the film. Annealing can be carried out under conditions as describedabove.

Conductive titanium oxide films may be used, for example, as aninterface layer between a high-k material and a metal electrode in amemory capacitor. In some embodiments, a memory capacitor suitable foruse in an integrated circuit is formed by a method comprising:

-   -   depositing a bottom electrode;    -   depositing a conductive titanium oxide layer doped with a group        V metal by ALD on the bottom electrode;    -   depositing an ultra-high-k layer directly over and contacting        the titanium oxide layer; and    -   depositing a top electrode directly over and contacting the        ultra-high-k layer.

FIG. 2 is a flow chart generally illustrating a method 200 for forming amemory capacitor in an integrated circuit in accordance with oneembodiment. The first illustrated step is to deposit a bottom electrode210. In some embodiments the bottom electrode is deposited by ALD. Thebottom electrode can be formed of any suitable material. In someembodiments, the bottom electrode comprises a noble metal, noble metaloxide or nitride, such as: Ru, RuO₂, IrO₂, W, Ir, Pt, SrRuO₃, Rh, Pd,Ag, Cu, Re, Os or Au or mixtures thereof or TiN, NbN, ZrN, HfN, MoN_(x),WN_(x), VN or TaN or mixtures thereof, etc.

Suitable precursors for ALD of noble metal containing electrodes aredescribed, for example, in U.S. Pat. No. 6,824,816 by Aaltonen et al andU.S. Patent Application Publication No. 2007-0014919 by Hamalainen etal. The disclosures of both are hereby incorporated by reference intheir entireties. Although Hamalainen et al describes noble metalprecursors in the context of noble metal oxide thin film deposition, thenoble metal precursors described are also suitable for the deposition ofnoble metal thin films.

Preferable Ti precursors for depositing TiN, Ti_(1−x)Nb_(x)N_(y) orTi_(1−x)Ta_(x)N_(y) electrodes include halides, cyclopentadienylcompounds, and cyclopentadienyl derivative compounds. Preferred halidesinclude compounds having the formula TiX₄, where X is a halogen, such asTiCl₄, TiBr₄, TiF₄, and TiI₄. Suitable nitrogen precursors include, butare not limited to: NH₃, NH₃-plasma and radicals, N₂/H₂-plasma andradicals, atomic N and H, and ammonia derivatives, such as hydrazine.

Preferably, the tantalum precursor for depositing TaN orTi_(1−x)Ta_(x)N_(y) electrodes includes halides or amine derivatives.Preferred halides include compounds having the formula TaX₅, wherein Xis a halide, such as TaCl₅, TaF₅, and TaBr₅. Preferred amine derivativesinclude alkylamines, for example pentakis(dimethylamino)tantalum(PDMAT), tertiary amyl imido-tris-dimethylamido tantalum (TAIMATA), andtert-butylimidotris(diethylamido)tantalum (TBTDET). Suitable nitrogenprecursors include, but are not limited to: NH₃, NH₃-plasma andradicals, N₂/H₂-plasma and radicals, atomic N and H, and ammoniaderivatives, such as hydrazine.

Preferably, the niobium precursor for depositing NbN orTi_(1−x)Nb_(x)N_(y) electrodes includes halides or amine derivatives.Preferred halides include compounds having the formula TaX₅, wherein Xis a halide, such as TaCl₅, TaF₅, and TaBr₅. Preferred amine derivativesinclude alkylamines, for example pentakis(dimethylamino)tantalum(PDMAT), tertiary amyl imido-tris-dimethylamido tantalum (TAIMATA), andtert-butylimidotris(diethylamido)tantalum (TBTDET). Suitable nitrogenprecursors include, but are not limited, NH₃, NH₃-plasma and radicals,N₂/H₂-plasma and radicals, atomic N and H, and ammonia derivatives, suchas hydrazine.

The next step is to deposit a conductive titanium oxide layer doped witha group V metal 220 by ALD on the bottom electrode. In some embodiments,there may be a layer between the bottom electrode and conductivetitanium oxide layer, such as an ultra-high-k layer. The deposition ofthe conductive titanium oxide layer 220 can include any of the methodsdescribed herein. The group V metal can include tantalum, niobium, andvanadium. Typically, the thin film formed in step 220 is annealed attemperatures above 500° C., and preferably above 600° C. As discussedabove, annealing changes the crystalline configuration of the dopedtitanium oxide thin film to an anatase crystalline configuration. Theanatase crystalline configuration has great conductive properties.Preferably, an ultra-high-k layer is then deposited in a process step230 directly over and contacting the conductive titanium oxide layer220. However, in some embodiments of a memory capacitor a dielectriclayer is not deposited between the conductive titanium oxide layer andtop electrode.

Preferably, the ultra-high-k layer comprises a material with adielectric constant greater than 10, more preferably greater than 20 andmost preferably greater than 40. In some embodiments the ultra-high-klayer has a dielectric constant greater than 100. More preferably, theultra-high-k layer comprises titanium, such as PbTiO₃,PbZr_(x)Ti_(1−x)O₃, SrTiO₃, BaTiO₃, SrBaTiO₃, BiTaO_(x) and SrBiTaO_(x)based compounds. In some embodiments the ultra-high K layer is depositedby ALD. Suitable precursors for the ALD of ultra-high k layers aredescribed, for example, in U.S. Pat. No. 7,108,747 to Leskela et al,U.S. patent application Ser. No. 10/696,591 by Vehkamaki et al, and inU.S. patent application Ser. No. 11/318,092 by Hatanpaa et al, which areall hereby incorporated by reference in their entirety.

Next, a top electrode is deposited 240 directly over and contacting theultra-high-k layer, thereby forming a memory capacitor. In someembodiments the top electrode is deposited by ALD. In some embodiments,the top electrode can comprise a noble metal or nitride, such as: Ru,RuO₂, IrO₂, W, Ir, Pt, SrRuO₃, Rh, Pd, Ag, Cu, Re, Os or Au or mixturesthereof or TiN, NbN, ZrN, HfN, MoN_(x), WN_(x), VN or TaN or mixturesthereof, etc.

Conductive titanium oxide films can also be used in other capacitorconfigurations. In some embodiments, a capacitor for use in anintegrated circuit is formed by a method comprising:

-   -   depositing a bottom electrode;    -   depositing a first conductive titanium oxide layer doped with a        group V metal by ALD on the bottom electrode;    -   depositing an ultra-high-k layer directly over and contacting        the first conductive titanium oxide layer;    -   depositing a second conductive titanium oxide layer doped with a        group V metal by ALD on the ultra-high-k layer; and    -   depositing a top electrode directly over and contacting the        second conductive titanium oxide layer.

In some embodiments, a capacitor for use in an integrated circuit isformed by the method comprising:

-   -   depositing a bottom electrode;    -   depositing an ultra-high-k layer directly over and contacting        the bottom electrode;    -   depositing a conductive titanium oxide layer doped with a group        V metal by ALD on the ultra-high-k layer; and    -   depositing a top electrode directly over and contacting the        conductive titanium oxide layer.

In other embodiments, a conductive titanium oxide layer in a capacitorstructure can be formed by oxidizing all or part of a doped titaniumnitride layer, as described above. In some embodiments, a doped titaniumnitride layer can be oxidized by providing an oxygen source in aseparate oxidation step. In other embodiments, a doped titanium nitridelayer can be oxidized during an annealing step or during deposition of asubsequent layer, such as a layer comprising an ultra-high-k material.

In some embodiments the doped titanium nitride layer is the bottomelectrode of a capacitor and during deposition of an overlyingultra-high-k layer, some fraction of the titanium nitride layer surfacemay oxidize to form an interfacial layer or interfacial composition ofconductive doped titanium oxide between the bottom electrode andultra-high-k layer. In some embodiments the Ti_(1−x)Nb_(x)O_(y) orTi_(1−x)Ta_(x)O_(y) functions as the electrode.

In some embodiments, a capacitor for use in an integrated circuit isformed by a method comprising:

-   -   depositing a layer comprising Ti_(1−x)Nb_(x)N_(y) or        Ti_(1−x)Ta_(x)N_(y);    -   depositing an ultra-high-k layer directly over and contacting        the layer comprising Ti_(1−x)Nb_(x)N_(y) or Ti_(1−x)Ta_(x)N_(y),        wherein an interfacial layer comprising conductive        Ti_(1−x)Nb_(x)O_(y) or Ti_(1−x)Ta_(x)O_(y) is formed between the        ultra-high-k layer and the Ti_(1−x)Nb_(x)N_(y) or        Ti_(1−x)Ta_(x)N_(y) layer from all or part of the        Ti_(1−x)Nb_(x)N_(y) or Ti_(1−x)Ta_(x)N_(y) layer; and    -   depositing a top electrode directly over and contacting the        ultra-high-k layer.

In some embodiments, a capacitor for use in an integrated circuit isformed by the method comprising:

-   -   depositing a layer comprising Ti_(1−x)Nb_(x)N_(y) or        Ti_(1−x)Ta_(x)N_(y);    -   depositing an ultra-high-k layer on top of the        Ti_(1−x)Nb_(x)N_(y) or Ti_(1−x)Ta_(x)N_(y), wherein a conductive        Ti_(1−x)Nb_(x)O_(y) or Ti_(1−x)Ta_(x)O_(y) interfacial layer is        formed by oxidizing at least a portion of the        Ti_(1−x)Nb_(x)N_(y) or Ti_(1−x)Ta_(x)N_(y); and    -   depositing a layer comprising Ti_(1−x)Nb_(x)N_(y) or        Ti_(1−x)Ta_(x)N_(y) on top of the ultra-high-k layer, wherein a        conductive Ti_(1−x)Nb_(x)O_(y) or Ti_(1−x)Ta_(x)O_(y) layer is        formed between the ultra-high-k layer and Ti_(1−x)Nb_(x)N_(y) or        Ti_(1−x)Ta_(x)N_(y) layer from all or part of the        Ti_(1−x)Nb_(x)N_(y) or Ti_(1−x)Ta_(x)N_(y) layer.

In some embodiments the Ti_(1−x)Nb_(x)N_(y) or Ti_(1−x)Ta_(x)N_(y) layeris oxidized during deposition of the ultra-high k layer.

In some embodiments, a capacitor for use in an integrated circuit isformed by the method comprising:

-   -   depositing a bottom electrode;    -   depositing an ultra-high-k layer on top of the bottom electrode;        and    -   depositing a layer comprising Ti_(1−x)Nb_(x)N_(y) or        Ti_(1−x)Ta_(x)N_(y) on top of the ultra-high-k layer and forming        a conductive Ti_(1−x)Nb_(x)O_(y) or Ti_(1−x)Ta_(x)O_(y) top        electrode over the ultra-high-k layer from all or part of the        Ti_(1−x)Nb_(x)N_(y) or Ti_(1−x)Ta_(x)N_(y).

Examples of suitable reactors that may be used include commerciallyavailable ALD equipment such as the F-120® reactor, Pulsar® reactor andAdvance® 400 Series reactor, available from ASM America, Inc of Phoenix,Ariz, and ASM Europe B.V., Almere, Netherlands. In addition to these ALDreactors, many other kinds of reactors capable of ALD growth of thinfilms, including CVD reactors equipped with appropriate equipment andmeans for pulsing the precursors can be employed. Preferably, reactantsare kept separate until reaching the reaction chamber, such that sharedlines for the precursors are minimized. However, other arrangements arepossible, such as the use of a pre-reaction chamber as described in U.S.application Ser. No. 10/929,348, filed Aug. 30, 2004 and Ser. No.09/836,674, filed Apr. 16, 2001, the disclosures of which areincorporated herein by reference.

The growth processes can optionally be carried out in a reactor orreaction space connected to a cluster tool. In a cluster tool, becauseeach reaction space is dedicated to one type of process, the temperatureof the reaction space in each module can be kept constant, whichimproves the throughput compared to a reactor in which is the substrateis heated up to the process temperature before each run.

A stand-alone reactor can be equipped with a load-lock. In that case, itis not necessary to cool down the reaction space between each run.

The following non-limiting examples illustrate certain preferredembodiments of the invention. They were carried out in an F-120™ ALDreactor supplied by ASM Microchemistry Oy, Espoo.

EXAMPLE 1

Alternating layers of TiO₂ and Nb₂O₅ were deposited by ALD from Ti(OMe)₄at 130° C. and water and Nb(OEt)₅ at 90° C. and water, respectively at215° C. By controlling the number of cycles of TiO₂ and Nb₂O₅deposition, the composition of the films was varied. FIG. 3 illustratescation ratios of TiNbO and TiTaO films as a function of ALD pulsingratio. The amorphous thin films formed by the ALD processes wereinsulators because no resistivity reading registered on the four pointprobe used to measure resistivity. Subsequently, the amorphous filmswere annealed in forming gas (5% H₂, 95% N₂) at 600° C. for 30 minutes.The thin films became conductive after annealing. Exemplaryresistivities for the various compositions are illustrated in FIG. 4. Aresistivity of 0.0019 Ωcm was measured for a Ti_(0.69)Nb_(0.31)O₂ film.

Additional data for the Ti_(0.69)Nb_(0.31)O₂ film is illustrated inFIGS. 5 and 6. FIG. 5 represents an x-ray diffractogram of an undopedTiO₂ film and a Ti_(0.69)Nb_(0.31)O₂ film. The undoped TiO₂ film iscloser to the x-axis and has a major peak around a 2θ value of about25°. The 52° peak is assumed to belong to the Si substrate. TheTi_(0.69)Nb_(0.31)O₂ film, illustrated further away from the x-axisshows major peaks at 2θ values of 25°, 37.5°, 48°, and 54°. All 2θvalues represent the anatase phase of titanium oxide. The anatase phasehas good electrical conductivity when doped with Nb.

The crystalline structure for a Ti_(0.69)Nb_(0.31)O₂ film is illustratedin FIG. 6, which is an emission scanning electron microscope (FESEM)image of the film after annealing at 600° C. in forming gas (5% hydrogen95% nitrogen). However, the crystallization behavior was unusual becausevery large grains with highly regular cross and wavy patterns wereformed. The image suggests that the film crystallized explosively, whichmight assist the crystallization of ultra-high-k layers.

Further analysis of the thin film via energy dispersive x-ray analysis(EDX) revealed that the composition of the film was very uniform. Crosspatterns could not be observed by atomic force microscopy (AFM), either.It is likely that the FESEM images are thus due to crystal orientationcontrast. Ti_(1−x)Nb_(x)O₂ thin films with x values in the range ofabout 0.20 to about 0.40 also exhibited similar crystallizationpatterns. As illustrated in FIG. 4, the film resistivity was also at aminimum around this range.

FIG. 7 is a graph illustrating the optical transmittance of aTi_(0.69)Nb_(0.31)O₂ film after annealing in forming gas at 600° C. Theoptical transmittance was measured using a UV/VIS-spectrometer. TheTi_(0.69)Nb_(0.31)O₂ thin film measured was formed on borosilicate glassand was approximately 42 nm thick. FIG. 7 illustrates that the TiNbOthin film has good optical transmittance of around 60% and higher in thevisible light spectrum, which is typically from around 380 nm to around750 nm. The transmittance of the bare borosilicate glass substrate isalso plotted in FIG. 7.

The crystalline properties of the TiNbO thin films were also measuredusing an x-ray diffractogram, as illustrated in FIG. 8. The d(101)values in angstroms for Ti_(1−x)Nb_(x)O₂ thin films with x values fromzero to about 0.4 are illustrated in FIG. 8. The d(101) values increaseas the Nb content increases in the thin films indicating good solubilityof Nb ions in TiO₂.

FIG. 9 illustrates resistivities for TiNbO thin films deposited at 300°C. without annealing (white squares), deposited at 215° C. and annealedin forming gas at 600° C. (circles), deposited at 300° C. and annealedin forming gas at 600° C. (squares), and deposited at 215° C. andannealed in nitrogen at 600° C. (triangles). The dashed line at thebottom of the graph illustrates the resistivity for ITO thin films ofabout 0.0002 Ω-cm. The film thickness generally increased with Nbcontent from about 44 nm for undoped TiO₂ to about 94 nm for the moreheavily doped TiNbO thin films. The amorphous TiNbO thin film (noannealing) typically had the highest resistivities. The annealed TiNbOthin films deposited at 215° C. had lower resistivity values than thefilm formed at 300° C. The TiNbO thin films annealed in forming gas hadslightly lower resistivities than those annealed in the presence ofnitrogen. The minimum resistivity measured was 0.0019 Ω-cm for aTi_(0.69)Nb_(0.31)O₂ thin film.

FIG. 10 illustrates resistivities of TiNbO thin films deposited onsilicon and borosilicate glass. The TiNbO thin films were deposited at215° C. using Ti(OMe)₄, Nb(OEt)₅, and water as Ti, Nb, and oxygenprecursors. The thin films were subsequently annealed for 30 minutes informing gas at 600° C. The lowest resistivity measure for the TiNbO thinfilm deposited on borosilicate glass was 0.0027 Ω-cm, higher than thelowest resistivity of 0.0019 Ω-cm measured for a TiNbO thin filmdeposited on silicon dioxide.

EXAMPLE 2

Amorphous layers of TiO₂ and Ta₂O₅ were deposited by ALD from Ti(OMe)₄at 130° C. and water and Ta(OEt)₅ at 105° C. and water, respectivelywith substrate temperatures around 215° C. Subsequently, the amorphousfilms were annealed in forming gas (5% H₂, 95% N₂) at greater than 600°C. forming a crystalline anatase phase film. By controlling the numberof cycles of TiO₂ and Ta₂O₅ deposition, the composition of the films wasvaried. No resistivity reading registered with the four point probe forthe amorphous thin films formed prior to annealing. Resistivities forthe three TiTaO compositions measured are illustrated in FIG. 4. Thethree Ti_(1−x)Ta_(x)O₂ thin films illustrated in FIG. 4 had x valuesbetween about 0.13 and about 0.30. The thin film with an x value about0.22 had the lowest resistivity of the illustrated TiTaO thin films.

EXAMPLE 3

An electrically conductive thin film can be used in a memory capacitor.First, a bottom electrode comprising ruthenium is deposited by an ALDtype process using Ru cyclopentadienyl compounds. The ALD processcomprises alternating and sequential pulses of a Ru precursor and anoxygen containing precursor. Next, a first conductive titanium oxidelayer is formed by the processes described herein. Next an ultra-high-klayer is deposited directly over and contacting the conductive TiO₂layer by an ALD process. The ultra-high-k layer is SrTiO₃ and isdeposited by alternating and sequential pulses of a strontiumcyclopentadienyl precursor, titanium alkoxide precursor and oxygenprecursor. Optionally, a second conductive titanium oxide layer is thenformed by the processes described herein. During the annealing step theamorphous titanium oxide layer crystallizes and becomes electricallyconductive. The ultra-high k layer can also crystallize during theannealing step. Typically, the ultra-high k layer has a k-value of morethan 50, and preferably more than 100 after the annealing step. The topelectrode, comprising ruthenium, is then deposited directly over andcontacting the optional second conductive titanium oxide layer ordirectly over and contacting the ultra-high-k layer in substantially thesame way as the bottom electrode.

EXAMPLE 4

Capacitor structures were also formed using TiNbO thin films depositedby the ALD processes described herein. A reference capacitor was firstformed on glass to compare the electrical performance of the TiNbOcapacitors. The reference capacitor was formed by first depositing anITO layer on the glass, then depositing an Al₂O₃ layer (about 86 nmthick) directly over and contacting the ITO, and finally depositing analuminum electrode directly over and contacting the Al₂O₃ layer.

A first test capacitor was formed on glass, by first depositing an ITOlayer. Next, an 80 nm thick TiNbO layer was deposited directly over andcontacting the ITO layer by the ALD processes described herein. Theamorphous TiNbO layer was then annealed to form a crystalline structure.Next, an Al₂O₃ layer (about 86 nm thick) was deposited directly over andcontacting the TiNbO layer. Finally, an aluminum electrode was formeddirectly over and contacting the Al₂O₃ layer. The electrical propertiesof the structure were suitable for use as a capacitor.

A second test capacitor was formed on silicon, by first growing asilicon dioxide layer approximately 150 nm thick. Next, a 100 nm thickTiNbO layer was deposited directly over and contacting the silicondioxide layer by the ALD processes described herein. Next, an Al₂O₃layer (about 86 nm thick) was deposited directly over and contacting theTiNbO layer. The TiNbO layer was annealed to form a crystallinestructure after deposition of the aluminum oxide layer. Finally, analuminum electrode was formed directly over and contacting the Al₂O₃layer. The electrical properties of the TiNbO layer were suitable foruse as a bottom electrode in a capacitor.

A third test capacitor was formed on silicon by first growing a silicondioxide layer approximately 150 nm thick. Next, a 100 nm thick TiNbOlayer was deposited directly over and contacting the silicon dioxidelayer by the ALD processes described herein. The amorphous TiNbO layerwas then annealed to form a crystalline structure. Next, an Al₂O₃ layer(about 86 nm thick) was deposited directly over and contacting the TiNbOlayer. Finally, an aluminum electrode was formed directly over andcontacting the Al₂O₃ layer. The electrical properties of the TiNbO layerwere suitable for use as a bottom electrode in a capacitor.

EXAMPLE 5

An electrically conductive Ti_(1−x)Nb_(x)O_(y) or Ti_(1−x)Ta_(x)O_(y)thin film can be formed by depositing Ti_(1−x)Nb_(x)N_(y) orTi_(1−x)Ta_(x)N_(y) and subsequently converting all or part of thenitride layer to oxide by treatment with an oxygen source chemical.

A layer comprising Ti_(1−x)Ta_(x)N_(y) or Ti_(1−x)Nb_(x)N_(y) is firstdeposited by an ALD type process using titanium, nitrogen, and dopantprecursors, such as TiCl₄, NH₃ and TaCl₅ or NbCl₅, respectively. Thetitanium deposition cycle comprises alternating and sequential pulses ofa Ti precursor, such as TiCl₄, and ammonia. The dopant deposition cyclecomprises alternating and sequential pulses of a Nb or Ta precursor,such as TaCl₅ or NbCl₅, and ammonia. The titanium deposition cycle anddopant deposition cycle are performed in a predetermined order based onthe desired composition of the thin films.

Next, the Ti_(1−x)Ta_(x)N_(y) or Ti_(1−x)Nb_(x)N_(y) thin film istreated with an oxygen containing reactant to form electricallyconductive thin films of Ti_(1−x)Nb_(x)O_(y) or Ti_(1−x)Ta_(x)O_(y).Suitable oxygen sources include, without limitation: water, ozone,oxygen, oxygen plasma, oxygen radicals, atomic oxygen, alcohol, andH₂O₂. An annealing step to enhance the crystallization of the oxidefilms may also be performed.

EXAMPLE 6

An electrically conductive thin film can be used in a memory capacitor.First, a bottom electrode comprising Ti_(1−x)Ta_(x)N_(y) orTi_(1−x)Nb_(x)N_(y) is deposited by an ALD type process using TiCl₄, NH₃and TaCl₅ or NbCl₅, respectively. The titanium deposition cyclecomprises alternating and sequential pulses of a Ti precursor, such asTiCl₄, and ammonia. The dopant deposition cycle comprises alternatingand sequential pulses of a Nb or Ta precursor, such as TaCl₅ or NbCl₅,and ammonia. The titanium deposition cycle and dopant deposition cycleare performed in a predetermined order based on the desired compositionof the thin films.

Next, an ultra-high-k layer comprising SrTiO₃ is deposited by an ALDprocess directly over and contacting the bottom electrode layercomprising Ti_(1−x)Ta_(x)N_(y) or Ti_(1−x)Nb_(x)N_(y). The SrTiO₃ultra-high-k layer is deposited by alternating and sequential pulses ofa strontium cyclopentadienyl precursor, titanium alkoxide precursor, andoxygen precursor.

During the first cycles of the ultra-high-k layer deposition, part ofthe Ti_(1−x)Ta_(x)N_(y) or Ti_(1−x)Nb_(x)N_(y) bottom electrode layer isoxidized and converted to a conductive Ti_(1−x)Nb_(x)O_(y) orTi_(1−x)Ta_(x)O_(y) layer. That is, the oxygen precursor in theultra-high-k layer deposition cycle can convert the surface of thebottom electrode from Ti_(1−x)Ta_(x)N_(y) or Ti_(1−x)Nb_(x)N_(y) toTi_(1−x)Nb_(x)O_(y) or Ti_(1−x)Ta_(x)O_(y).

During an annealing step the oxidized surface of the Ti_(1−x)Ta_(x)N_(y)or Ti_(1−x)Nb_(x)N_(y) layer crystallizes more. The increasedcrystallization of the doped titanium nitride layer typically results inincreased electrical conductivity.

The crystallinity of the ultra-high-k layer can also increase during theannealing step. Typically, the ultra-high k layer has a k-value of morethan 50, and preferably more than 100 after the annealing step. A topelectrode can be deposited on the ultra-high-k layer before or after anannealing step.

The methods disclosed herein provide many advantages over those known inthe art. Embodiments of the methods disclose reliable and controllablemethods for forming conductive titanium oxide thin films using an ALDprocess. The benefits of controllable and self limiting ALD processesare well known. The titanium oxide thin films are particularly wellsuited for use in memory capacitors. The conductive titanium oxide thinfilms also complement dielectric layers comprising titanium.

It will be appreciated by those skilled in the art that variousmodifications and changes can be made without departing from the scopeof the invention. Similar other modifications and changes are intendedto fall within the scope of the invention, as defined by the appendedclaims.

We claim:
 1. A process for producing a doped titanium oxide thin film ona substrate in a reaction chamber by atomic layer deposition, theprocess comprising: a titanium oxide deposition cycle comprising:providing a vapor phase reactant pulse comprising a titanium precursorinto the reaction chamber to form no more than about a single molecularlayer of the titanium precursor on the substrate; removing excessreactant from the reaction chamber, if any; providing a vapor phasereactant pulse comprising an oxygen precursor to the reaction chambersuch that the oxygen precursor reacts with the titanium precursor on thesubstrate; removing excess second reactant and any reaction byproductsfrom the reaction chamber; and a dopant oxide deposition cyclecomprising: providing a vapor phase reactant pulse comprising a niobiumor tantalum precursor to the reaction chamber; removing excess reactantfrom the reaction chamber; providing a vapor phase reactant pulsecomprising an oxygen precursor to the reaction chamber such that theoxygen precursor reacts with the niobium or tantalum precursor on thesubstrate; removing excess reactant and any reaction byproducts from thereaction chamber; wherein the titanium oxide cycle and dopant oxidecycles are repeated until a thin film of a desired thickness andcomposition comprising Ti_(1−x)Nb_(x)O_(y) or Ti_(1−x)Ta_(x)O_(y) isobtained, wherein x is between 0 and 1, wherein y is about 2; whereinthe doped titanium oxide thin film is electrically conductive; andwherein the doped titanium oxide thin film is in direct contact with adielectric layer in a semiconductor device.
 2. The method of claim 1,wherein the oxygen source comprises one or more of water, ozone, H₂O₂,alcohol, atomic oxygen, oxygen radicals and oxygen plasma.
 3. The methodof claim 1, wherein the niobium source comprises Nb(OEt)₅.
 4. The methodof claim 1, wherein the tantalum source comprises Ta(OEt)₅.
 5. Themethod of claim 1, wherein the Nb or Ta x value is between about 0.01and about 0.5.
 6. The method of claim 1, wherein the Nb or Ta x value isbetween about 0.20 and about 0.35.
 7. The method of claim 1, wherein theNb x value is about 0.31.
 8. The method of claim 1, wherein the thinfilm has a thickness between about 2 nm and about 200 nm.
 9. The methodof claim 1, wherein the substrate temperature is between about 200° C.and about 350° C. during the providing and removing steps.
 10. Themethod of claim 1, wherein the substrate temperature is between about200° C. and about 250° C. during the providing and removing steps. 11.The method of claim 1, further comprising annealing the thin film byheating the substrate.
 12. The method of claim 11, wherein whenannealing the substrate is heated to a temperature above 500° C.
 13. Themethod of claim 11, wherein when annealing the substrate is heated to atemperature above 600° C.
 14. The method of claim 11, further comprisingproviding a reducing gas mixture during annealing.
 15. The method ofclaim 11, further comprising providing hydrogen gas during annealing.16. The method of claim 11, wherein the annealing step thereby producesan anatase crystalline thin film.
 17. The method of claim 11, whereinthe thin film has a resistivity less than about 0.01Ω-cm.
 18. The methodof claim 11, wherein the thin film has a resistivity less than about0.005Ω-cm.
 19. The method of claim 11 wherein the thin film producedthereby has an optical transmittance of greater than about 60% in thevisible region.
 20. The method of claim 1, wherein a high-k structure isdeposited directly over and contacting the thin film.
 21. The method ofclaim 20, wherein the high-k structure comprises titanium.
 22. Themethod of claim 20, wherein the high-k layer comprises one or more ofPbTiO₃, PbZr_(x)Ti_(1−x)O₃, SrTiO₃, BaTiO₃, SrBaTiO₃, BiTaO_(x) andSrBiTaO_(x).
 23. The method of claim 20, further comprising depositing aconductive doped titanium oxide thin film on the high-k structure. 24.The method of claim 23, wherein the high-k layer includes titanium. 25.The method of claim 23, wherein the high-k layer comprises one or moreof PbTiO₃, PbZr_(x)Ti_(1−x)O₃, SrTiO₃, BaTiO₃, SrBaTiO₃, BiTaO_(x) andSrBiTaO_(x).
 26. The method of claim 1, wherein the Ti_(1−x)Nb_(x)O_(y)or Ti_(1−x)Ta_(x)O_(y) thin film is conductive.
 27. The method of claim1, wherein the niobium or tantalum precursor comprises an organicligand.